A 52-year-old man is brought to the trauma center 30 minutes after a fall from a 15-foot ladder. On arrival, GCS is 8/15 (E2V2M4). He is intubated in the field by paramedics for airway protection. CT head shows a 4 cm acute subdural hematoma with 8 mm midline shift and uncal herniation signs. Blood pressure is 160/95 mmHg, heart rate 58/min, respiratory rate 12/min on mechanical ventilation. What is the most appropriate immediate next step in management?